Our genomes are mostly made up of repetitive 'junk DNA' derived from insertions of mobile elements. Our group has developed methods to identify polymorphic insertions of these understudied sequences, demonstrated they are major sources of structural variation our genome, and found they occur frequently in linkage disequilibrium with trait associated SNPs identified by GWAS. Experiments by others and characterizations of the non-random distribution of mobile DNAs in genomes indicate they have significant potential to effect gene function. Our overarching hypothesis is that a subset of Alu insertions - the most prevalent and polymorphic mobile DNAs in humans - has phenotypic consequence. Our specific objectives are to isolate and characterize the effects of two polymorphic Alu insertions in allelogenic transgenic mouse models. The first insertion polymorphism to be studied is an intronic Alu 287bp in the angiotensin converting enzyme (ACE) gene locus. ACE encodes a key component of the renin-angiotensin-aldosterone blood pressure control system and is also involved in vascular homeostasis through degradation of bradykinin; the Alu is a well-studied marker of reduced ACE enzyme levels and presumed to be functional, although this has not been directly tested. The second polymorphism we propose to study is a 168bp intronic Alu insertion in the AT-rich interactive domain-containing protein 5B (ARID5B) locus. We recently associated this polymorphic Alu with risk for developing the most common childhood cancer, precursor B-cell acute lymphoblastic leukemia (ALL). The proposed studies will be the first to isolate and measure effects common, naturally-occurring TE insertion polymorphisms in vivo and to generate models to study mechanisms of these effects. More broadly, the work will provide a study design for mouse modeling in GWAS follow-up and begin work to make available an allelogenic YAC resource for studying functions of other Alu insertions.